An endangered species of horse -- known as Przewalski's horse -- is much more distantly related to the domestic horse than researchers had previously hypothesized, reports a team of investigators led by Dr. Kateryna Makova, a Penn State University associate professor of biology. The scientists tested the portion of the genome passed exclusively from mother to offspring -- the mitochondrial DNA -- of four Przewalski's horse lineages and compared the data to DNA from the domestic horse (Equus caballus). They concluded that, although previous scientists had assumed that Przewalski's horse and the domestic horse had diverged around the time that horses were domesticated -- about 6,000 to 10,000 years ago -- the real time of the two species' divergence from one another is much more ancient. The data gleaned from the study also suggest that present-day Przewalski's horses have a much more diverse gene pool than previously hypothesized. The new study's findings could be used to inform conservation efforts to save the endangered horse species, of which only 2,000 individuals remain in parts of China and Mongolia, and in wildlife reserves in California and the Ukraine. The paper will be published in the journal Genome Biology and Evolution. It was first published online, before print, on July 29, 2011. Przewalski's horse -- a stocky, short-maned species named after a Russian explorer who first encountered the animal in the wild -- became endangered during the middle of the last century when the species experienced a population bottleneck -- an evolutionary event in which many or most members of a population or a species die. "Sadly, this bottleneck was the result of human activity," Dr. Makova explained.